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Bureau of Mines Information Circular/1988 



Effectiveness of Catalytic Converters 
on Diesel Engines Used 
in Underground Mining 

By B. T. McClure, K. J. Baumgard, and W. F. Watts, Jr. 




^ tNT 0r '♦ 



UNITED STATES DEPARTMENT OF THE INTERIOR 




Information Circular 9197 



Effectiveness of Catalytic Converters 
on Diesel Engines Used 
in Underground Mining 



By B. T. McClure, K. J. Baumgard, and W. F. Watts, Jr. 
ii 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
T S Ary, Director 







Library of Congress Cataloging in Publication Data: 



McCIure, B. T. (B. Thompson) 

Effectiveness of catalytic converters on diesel engines useu in underground mining. 

(Information circular; 9197) 

Bibliography: p. 10-12. 

Supt. of Docs, no.: I 28.27:9197. 

1. Mining machinery—Catalytic converters. 2. Diesel motor exhaust gas- 
Purification. I. Baumgard, K. J. (Kirby, J.). II. Watts, W. F. (Winthrop F.). 
III. Title. IV. Series: Information circular (United States. Bureau of 

Mines); 9197. 



-TN295.U4 



[TN345] 



622 s [6221.8] 



88-600120 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Commercial converters 2 

Oxidizing catalytic converters 2 

Quantitative evaluation of catalytic converters 3 

Engine operation test results 3 

Catalytic converter performance over time 6 

In-mine tests 6 

Discussion 7 

Conclusions and recommendations 10 

References 10 

Appendix. — Abbreviations and symbols used in this report 13 

ILLUSTRATIONS 

1. Carbon monoxide and total hydrocarbon reduction as function of converter 

temperature 4 

2. Nitrogen dioxide emission as function of converter temperature 4 

3. Sulfate and sulfur dioxide emissions as function of converter temperature. . . 5 

TABLES 

1. Exposure limits for diesel exhaust pollutants 2 

2. Catalytic converter emission reductions 7 

3. Effect of catalytic converters on EQI 9 







UNIT OF MEASURE ABBREVIATIONS USED 


IN THIS REPORT 


°c 




degree Celsius 


m 3 


cubic meter 


ft 




foot 


mg/m 3 


milligram per cubic meter 


g 




gram 


min 


minute 


g/h 




gram per hour 


mm 


millimeter 


g/kW« 


h 


gram per kilowatt hour 


pet 


percent 


h 




hour 


ppm 


part per million 


L 




liter 


s 


second 



EFFECTIVENESS OF CATALYTIC CONVERTERS ON DIESEL ENGINES 

USED IN UNDERGROUND MINING 

By B. T. McClure, 1 K. J. Baumgard, 2 and W. F. Watts, Jr. 3 



ABSTRACT 

Oxidizing catalytic converters are sometimes used by underground mine 
operators as an emission control device to reduce odor, hydrocarbon 
(HC), and carbon monoxide (CO) emissions from diesel equipment. The 
objectives of this report are to quantitatively assess the effects of 
catalytic converters on diesel exhaust emissions and to make recommenda- 
tions for their use. Information in this report is from a literature 
survey and contract research supported by the Bureau of Mines. 

Catalytic converters are effective in reducing CO, HC, and odors when 
the exhaust temperature is high enough so that the converter remains 
above 250° C. Converter temperature is dependent upon engine duty cy- 
cle. Catalytic converters increse sulfate emissions and slightly in- 
crease oxides of nitrogen (N0 X ) emissions. If low sulfur fuels are not 
used, the increase in sulfate and nitrogen dioxide (N0 2 ) emissions can 
offset any advantages of the catalytic converter as measured by the 
emissions quality index (EQ1). In addition, in vitro bioassays have 
shown that catalytic converters produce soluble organic compounds, which 
have increased mutagenic activity with respect to untreated exhaust. 

Based upon criteria recommended by a joint Canadian-United States re- 
search panel, catalytic converters should only be used in special cir- 
cumstances in underground mines. Vehicles equipped with catalytic con- 
verters should operate under moderate to heavy load conditions, and use 
fuel with a sulfur content less than 0.1 pet. 



^ Research physicist. 
^Mechanical engineer. 
■^Industrial hygienist. 
Twin Cities Research Center, Bureau of Mines, Minneapolis, MN . 



INTRODUCTION 



This Bureau of Mines report quantita- 
tively assesses the effects of catalytic 
converters on diesel exhaust emissions 
and makes recommendations for their use. 
Information in this report is from a lit- 
erature survey and contract research sup- 
ported by the Bureau. 

Diesel-powered equipment is widely used 
in underground metal and nonmetal mines 
and its use in coal mines is increasing 
0_). 4 It is widely believed that diesels 
are more flexible, economical to operate, 
and are able to boost productivity over 
that of their electrically powered (bat- 
tery, tethered, or trolly) counterparts 
(2). 

However, diesel engines emit pollutants 
that reduce overall air quality. Pollut- 
ants emitted in diesel exhaust include 
CO, carbon dioxide (C0 2 ), HC, nitric 
oxide (NO), N0 2 , sulfur dioxide (S0 2 ), 
and diesel particulate matter (DPM). 
Such pollution is particularly undesir- 
able in a restricted environment as in an 
underground mine. Concentrations of CO, 
C0 2 , NO, N0 2 , and S0 2 are regulated by 
the Mine Safety and Health Administra- 
tion. The standards are shown in table 
1. DPM has no specific standard at this 
time, however, in coal mines DPM is in- 
directly regulated under the 2 mg/m 3 re- 
spirable dust standard. 

TABLE 1. - Exposure limits for diesel 
exhaust pollutants 



Pollutant 


Noncoal 


Coal 




FSEL 


STEL 


FSEL 


STEL 


CO. . . . ppm. . 
C0 2 • • • ppm. . 
NO. . . .ppm. . 
N0 2 . . .ppm. . 
S0 2 . • .ppm. . 


50 

5,000 

25 

NAp 

5 


400 

15,000 

37.5 

5 

20 


50 

5,000 

25 

3 

2 


400 

30,000 

NAp 

5 

5 



FSEL Full-shift exposure limit. 

NAp Not applicable. 

STEL Short-term exposure limit. 

Because of the usefulness of diesels it 
is desirable to control their emissions, 



and catalysts are one method. Mine oper- 
ators have been using catalytic conver- 
ters in underground mines for more than a 
decade to reduce CO, HC 03), and odor, 
which is primarily associated with HC's 
(4_). Converter use is prohibited in some 
areas of gassy noncoal mines, and coal 
mines, because of their high operating 
temperatures. Examples of these areas 
include the cutting face and return air- 
ways where gas and dust concentrations 
may be high and where permissible equip- 
ment is required. 

COMMERCIAL CONVERTERS 

Oxidizing catalytic converters are sold 
commercially for several applications, 
including wood-burning stoves, natural 
gas burners, and for heavy-duty diesel 
engines used in mining. The precious 
metals that are used as catalysts include 
platinum, palladium, and others, which 
are bonded to the surface of a substrate 
where the chemical reactions take place. 

Converters used on underground diesels 
in the United States are typically one 
of two types, monolithic substrate or 
pellet-type. The monolithic converter 
uses a ceramic, monolithic honeycomb sub- 
strate to support the catalyst. The 
monolith has many small axial passages 
that extend the length of the honeycomb, 
and are separated from one another by 
thin porous walls approximately 0.15- to 
0.3-mm thick. The monolith is usually 
cylindrical, sized to accommodate the ex- 
haust flow of the engine, and enclosed in 
a stainless steel container adapted to 
fit the exhaust system. 

The pellet-type converter uses spheri- 
cal or cylindrical pellets, approximately 
3 mm in diam which fit into a stain- 
less steel container sized to fit the ex- 
haust system. A typical pellet converter 
is larger and heavier than a monolithic 
converter. 

OXIDIZING CATALYTIC CONVERTERS 



^Underlined numbers in parentheses re- 
fer to items in the list of references 
preceding the appendix. 



An oxidizing catalytic converter is 
placed as near as possible to the ex- 
haust manifold to ensure that hot exhaust 



gases pass over the catalyst at maximum 
temperature. The performance of conver- 
ters is critically dependent on the ex- 
haust temperature, which depends upon en- 
gine operation. If an engine is operated 
at low load, the low exhaust temperature 
allows soot to accumulate on the catalyst 
surface, thereby restricting access of 
the exhaust to the catalyst and inhibit- 
ing the desired oxidation. As the hot 
gases pass over the catalyst, oxidation 
of CO and HC to C0 2 , water vapor takes 
place, thus reducing the amount of CO, 
HC, and offensive odors in the exhaust 
stream. At high exhaust temperatures the 
converter also oxidizes S0 2 and NO to 
more toxic sulfuric acid (H2SO4) and N0 2 
(5-2)- 

Research conducted by the Engelhard 
Corp. , Edison, NJ, under a Bureau 



contract (7) demonstrated that converter 
effectiveness is temperature dependent 
and that high-temperature operation in- 
creases N0 2 emissions. Figure 1 shows 
that greater than 50 pet reductions in 
CO and HC ems s ions can be achieved 
when catalyst temperatures exceed 250° C. 
This temperature is not achieved unless 
the engine is operated at moderate to 
high loads. Figure 2 shows that above 
300° C this particular catalyst signifi- 
cantly increased the emission of N0 2 . 
This occurs because at the higher temper- 
atures the oxidation of NO to N0 2 is 
enhanced. Figure 3 shows that S0 2 is 
oxidized to S0 4 at catalyst temperatures 
above 300° C. S0 4 emissions are depen- 
dent upon fuel sulfur content and can be 
minimized by using fuel that has a sulfur 
content of less than 0.1 pet. 



QUANTITATIVE EVALUATION OF CATALYTIC CONVERTERS 



Laboratory tests have been performed by 
government agencies, private industry, 
and others to determine the effective- 
ness of using converters as an emis- 
sion control device. These tests can be 
classified in categories; steady-state, 
transient, durability, and in-mine. 
Steady-state tests are performed by oper- 
ating the engine at constant load and 
speed conditions and do not include 
periods of acceleration or deceleration. 
Transient engine tests, on the other 
hand, have periods of changing load and 
speed conditions, and more closely sim- 
ulate equipment operation. Durability 
tests evaluate the long-term effective- 
ness of converters and in-mine tests 
evaluate the performance under actual 
working conditions. 

ENGINE OPERATION TEST RESULTS 

Eccleston (8_) tested a monolithic con- 
verter on a Deutz F6M-212W engine using 
the Environmental Protection Agency 13- 
mode heavy-duty test cycle and No. 2 
diesel fuel containing 0.20 pet sulfur. 
Emissions were measured before and after 
the converter. The results show that for 
the heavy-load conditions the converter 
decreased HC by 33 pet, CO by 78 pet, 
while N0 2 increased by 12 pet and S0 4 
increased from 2.3 ppm to 25 ppm (983 



pet). Under light-load conditions, HC 
decreased 28 pet, CO decreased 39 pet, 
SO4 decreased 10 pet, and there was no 
significant change in N0 2 . The average 
results over all 13 modes showed, that HC 
decreased 35 pet, CO 63 pet, N0 2 12 pet, 
and SO4 increased 455 pet. These tests 
were repeated for a Deutz F6L-912W engine 
with similar results. 

Acres (9) evaluated a ceramic substrate 
platinum catalyst at three different con- 
ditions; idle, medium, and heavy loads. 
At idle load and speed the catalyst had 
no effect on CO emissions, at medium 
loads the conversion efficiency was 80 
pet, and at high loads the conversion 
efficiency was 84 pet. Acres also mea- 
sured the N0 X concentration and found no 
significant effects. 

Sercombe (10) tested the effectiveness 
of two platinum catalysts using a direct- 
injection diesel engine following the 
California Air Resources Board 13-mode 
cycle. Emissions were observed in each 
mode, and cycle weighted averages were 
obtained. The results from the first 
catalyst tested indicate that the HC 
emissions decreased 68 pet and the CO 
emissions decreased 90 pet. The tests of 
a second catalyst showed a reduction of 
HC emissions of 64 pet and CO emissions 
of 87 pet. Neither catalyst showed a 
significant change in N0 2 emissions. 



100 




KEY 
O Carbon monoxide 
A Total hydrocarbons 



150 



200 250 300 350 400 

CATALYST TEMPERATURE, °C 



450 



500 



550 



FIGURE 1. -Carbon monoxide and total hydrocarbons reduction as function of converter temperature. 



1 40 




1 50 200 250 300 350 400 

CATALYST TEMPERATURE, °C 



450 



500 



550 



FIGURE 2. -Nitrogen dioxide emission as function of converter temperature. 



cn 



LU 
< 

or 

O 

co 

CO 

LU 
CM 

o 

CO 
"O 

c 
o 

O 
CO 



.2 - 



1.0 - 



.8 - 



.6 - 



.4 - 



.2 - 







1 1 1 




1 

KEY 


l 


1 ° 


S0 4 (sulfate) 




1 A 


S0 2 


(sulfur di 


oxide) 


\ 


A 




- 


- 




A ^* 


^Sw 


1 1 1 




i 


1 



150 200 250 300 350 400 

CATALYST TEMPERATURE, °C 

FIGURE 3. -Sulfate and sulfur dioxide emissions as function of converter temperature. 



450 



Evaluation of catalytic converters op- 
erated under steady-state engine condi- 
tions has shown that a high conversion 
efficiency of CO occurs when the engine 
is operated at high engine loads, but 
that the efficiency is significantly less 
for the lighter loads. Sulfate emissions 
are greatly increased by the converter 
for the heavy loads, but not for the 
light loads. 

Bykowski (11) tested an eight-cylinder, 
indirect-injection, 5. 7-L diesel engine 
equipped with a monolithic converter us- 
ing the transient Federal test procedure 
and fuel with 0.29 pet sulfur. The cata- 
lyst decreased the emission of CO by 
approximately 90 pet and HC by approxi- 
mately 60 pet. A slight increase in N0 X 
emissions and a 500-pct increase in 



sulfate emissions were observed. The 
same data were collected after the vehi- 
cle had been operated 190 miles. No 
change in converter operation was de- 
tected. During the tests, the maximum 
temperature at the converter inlet was 
196° C and the minimum temperature was 
76° C. 

Steady-state data were used to estimate 
the cycle emissions for a mining load- 
haul-dump (LHD) vehicle equipped with a 
Deutz F6L 714 engine and a PTX 623 mono- 
lithic converter (5). The cycle was 
divided into six steady-state modes, each 
of different duration. The total time 
for one complete cycle was 210 s. The 
emissions, before and after the conver- 
ter for each of the six modes, were aver- 
aged over time to yield integrated values 



for each pollutant for the entire cycle. 
The converter removed 85 pet of the CO 
and caused a small reduction in NO with a 
corresponding increase in N0 2 . A small 
increase in DPM was accompanied by a de- 
crease in S0 2 with a corresponding 44-pct 
increase in H 2 S0 4 . 

The efficiency of a clean converter de- 
pends mainly upon the temperature of the 
catalyst, which in turn is dependent on 
the duty cycle. Figure 1 shows 50 pet 
conversion of CO and HC occurs at about 
190° and 250° C, respectively. As higher 
temperatures are attained, the conversion 
efficiency increases. At low exhaust 
temperatures, soot and carbon accumulate 
on the converter substrate and perfor- 
mance degrades rapidly. 

Tests of catalytic converters operated 
under transient test conditions resulted 
in increased N0 2 emissions. DPM emis- 
sions were increased by the formation 
of S0 X through oxidation of fuel sulfur. 
This can be mitigated if low-sulfur fuel 
is used. 

CATALYTIC CONVERTER PERFORMANCE OVER TIME 

The durability of a monolithic conver- 
ter was investigated by Fleming (12). 
Tests were conducted on a naturally aspi- 
rated, direct-injection, 10.4-L displace- 
ment diesel engine using fuel with 0.14 
pet sulfur. During the evaluation NO 
emissions were reduced by retarding the 
injection timing by three degrees and by 
employing exhaust gas recirculation. To 
reduce CO and HC emissions, a monolithic 
platinum converter was installed on each 
bank of cylinders. The injection nozzles 
were modified to aid in lowering HC emis- 
sions. At 125-h intervals, the emis- 
sions of CO, HC, and N0 2 were measured 
for thirteen 10-min periods and averaged. 
Samples of the exhaust were taken up- 
stream of the converter during the first 
5 min and downstream of the converter for 
the last 5 min during each period. The 
results indicated that the converter oxi- 
dized about 90 pet CO at the beginning of 
the test and about 88 pet after 1,060 h. 
Initially, 70 pet of the HC's were con- 
verted, but after 1,060 h only 60 pet 
were converted. The converters caused a 
small increase in fuel consumption, and 



smoke emissions increased slightly with 
operating time. 

Marshall (13-14) tested several cata- 
lysts to determine their efficiency in 
oxidizing CO and HC, and also tested a 
platinum-based pellet-type converter for 
durability. For these tests, a duty 
cycle was chosen to simulate the opera- 
tion of a utility vehicle with an overall 
load factor approximately 25 pet. The 
converter was most effective at reducing 
CO and HC concentrations when operated 
above 300° C and maintained a relatively 
constant conversion efficiency for the 
first 1,000 h. After that time, the CO 
and HC emissions increased both before 
and after the converter. The increase 
was attributed to fuel-injection nozzle 
malfunctions, such as a poor spray pat- 
tern or leakage of the injectors. 

Inadequate engine maintenance can ad- 
versely affect emissions and degrade cat- 
alytic converter performance (15). All 
catalysts tested greatly increased the 
emissions of SO3 and these increases were 
related to the fuel sulfur content. Be- 
cause of these increased emissions, the 
investigators recognized that other con- 
trol measures, such as ceramic particle 
filters or water scrubbers, might have to 
be used in conjunction with catalyst sys- 
tems to ensure satisfactory performance. 

These evaluations establish that cata- 
lytic converters maintain their perfor- 
mance up to 1,000 h under laboratory con- 
ditions, proper engine maintenance is 
required for best performance. 

IN-MINE TESTS 

A West German research group installed 
PTX-4D and 6D monolithic converters on 
mining vehicles (16) , which were peri- 
odically taken out of service and checked 
for emissions after operation in two 
drifts. Drift A had eight PTX-4D cata- 
lysts and a total of 18,500 h of opera- 
tion were accumulated on the eight 
converters for an average of 3,083 h 
each. Two converters failed during this 
test after 925 and 1,732 h, respectively. 
In drift B, one PTX-6D failed after 
1,436 h and two PTX-4D failed after 1,156 
and 1,432 h, respectively. The engines 
equipped with PTX-4D converters should 



have used the larger PTX-5D, but because 
of space constraints the 4D's were sub- 
stituted. This may explain the high 
failure rate of the 4D's. The remaining 
eight PTX-6D's accumulated 17,500 h of 
operation for an average of 2,188 h each. 
The converters were tested under two 
conditions, partial load and full load. 
For the PTX-4D, the initial conversion 
efficiency was 87 pet for CO, which de- 
creased to 65 pet after 200 operating h. 
The efficiency dropped to 30 pet between 
1,000 to 1,500 operating h at which point 
the converters were cleaned by burning 
off the collected soot at high temper- 
atures, a process called regeneration. 
Regeneration resulted in improved effi- 
ciency, but the initial conversion 



efficiency was not restored. The PTX-6D 
converter tested at full load had an ini- 
tial CO conversion efficiency of 90 pet, 
which gradually decreased to 50 pet after 
2,000 operating h. 

Table 2 summarizes the catalytic con- 
verter test results reported in the lit- 
erature. These results were obtained on 
a variety of engines operated under dif- 
ferent conditions, with different types 
of catalytic converters. Specific infor- 
mation can be obtained from the reference 
cited. 

The average reduction for CO was 77 pet 
and 54 pet for HC for all tests summar- 
ized in table 2. The results for N0 2 and 
S0 4 indicate an increase in emissions. 



TABLE 2. - Catalytic converter emission reductions, percent 



CO 



HC 



NO- 



SO, 



CO 



HC 



NO- 



SO, 



Reference 4. , 
Reference 8. . 

Reference 9. . 
Reference 10. 



85 
63 
78 
39 
80 
84 
90 
87 



NG 
35 
33 

28 
NG 
NG 
68 
64 



INC 
12 

+ 12 
NC 
NC 
NC 
NC 
NC 



'+441 

+455 

+ 983 

+ 10 

NG 

NG 

NG 

NG 



Reference 11. 
Reference 12. 

Reference 14. 

Reference 16. 

Reference 17. 



90 
90 
88 
2 752 
2 802 
87 
30 
90 



60 

70 

60 

2772 

2 452 
NG 
NG 
NG 



NC 
NG 
NG 
NG 
NG 
NG 
NG 
+ 25 



+ 500 
NG 
NG 
NG 
NG 
NG 
NG 
+4,251 



+ Percent increase. 
INC Increased. 
NC No change. 



NG Not given. 
1 Measured as H 2 S0 4 . 
Approximate values. 



DISCUSSION 



Diesel exhaust contains many sub- 
stances, each of which may be affected 
by the use of a control device. To 
ensure that the use of a specific device 
to control one pollutant does not lead to 
an overall degradation of emissions, some 
means to judge the overall effectiveness 
of a treatment device is required. In 
1981, three criteria were recommended by 
a joint Canadian-United States research 
panel (18). These were (1) an index for 
ventilation, (2) the Ames bioassay, which 
tests for mutagenicity, is one indicator 
of potential carcinogenity , and (3) mea- 
surement of the concentrations of six 
polycyclic aromatic HC, some of which 
are known carcinogens. These criteria 
are used to evaluate catalytic control 
systems. 



The air quality index (AQI) was formu- 
lated (19) to provide a single qualita- 
tive indicator of the risk associated 
with exposure to diesel emissions. AQI 
was defined as, 

AQI - (C0)/TLV for CO 

+ (N0)/TLV for NO 

+ (RCD)/TLV for RCD 

+ 1.5 [(S0 2 )/TLV for S0 2 

+ (RCD)/TLV for RCD] 

+1.2 [(N0 2 ) /TLV for N0 2 

+ (RCD)/TLV for RCD], 



where the gaseous components are ex- 
pressed in parts per million and respi- 
rable combustible dust (RCD) is expressed 
in milligrams per cubic meter. In prac- 
tice AQI is determined at different loca- 
tions in the mine, and AQI decreases as 
the exhaust is diluted. 

The denominator values for 



N0 2 , and S0 2 were originally 



CO, NO, 
the 1978 
of Gov- 
(ACGIH) 
The cur- 



recommended American Conference 
ernmental Industrial Hygienists 
threshold limit values (TLV). 
rent TLV's should be used; 50 ppm for CO, 
25 ppm for NO, 3 ppm for N0 2 , and 2 ppm 
for S0 2 (20). There is no TLV for RCD 
so the respirable coal mine dust standard 
of 2.0 mg/m 3 was proposed for RCD. The 
index applies the ACGIH additive princi- 
ple for the presence of multiple pollut- 
ants (20) and incorporates two factors, 
1.5 and 1.2, to account for possible syn- 
ergistic effects. 

It was suggested that ( 19 ) an AQI value 
between 3 and 4 be interpreted as pos- 
ing a moderate health risk, and a value 
greater than 4 poses a serious health 
threat, which required either reductions 
in pollutant concentrations or increased 
ventilation. In any case no individual 
pollutant should exceed its TLV. For 
more detailed information on the AQI 
refer to references 19 and 21 through 23. 

Mogan (24) extended the use of the AQI 
by applying the definition to raw and 
treated diesel exhaust and refers to this 
measure as the EQI. Since the goal for 
the AQI value in underground mines was 3, 
measuring the concentrations of the con- 
taminants at the exhaust pipe with and 
without emission controls, calculating 
the EQI, and dividing by 3 provides an 
estimate of the number of equivalent vol- 
umes of fresh air needed to dilute the 
exhaust to achieve an acceptable AQI. 
This application of the EQI assumes that 
the chemical composition and quantity of 
exhaust products does not change with 
dilution. 

Mogan (17) reported that the EQI for 
a bare engine was 215; for a converter 
equipped engine it was 397. The higher 
EQI was mainly due to the increase in RCD 
caused by the increase in sulfate. Sul- 
fate emissions are directly related to 
the fuel sulfur content, and the increase 



in RCD owing to an increase in sulfates 
can be minimized by using a low-sulfur 
fuel. The fuel used in these tests con- 
tained 0.25 pet sulfur. Diesel fuel with 
less than 0. 1 pet sulfur content should 
be used to minimize sulfate emissions (6, 
25). 

Similar tests were performed (_5) on a 
Deutz F6L 714 and a Detroit 8V71N diesel 
engines equipped with monolithic conver- 
ters. The emissions were measured for 
each mode and averaged to yield inte- 
grated values that were substituted into 
the EQI expression. For the Deutz en- 
gine, the EQI increased from 140 to 417 
when the converter was used, and it 
increased by a factor of 2.5 for the 
Detroit engine. The increase in the AQI 
was due to increases in the emissions of 
N0 2 and sulfates. 

Mogan (26) summarized estimates derived 
from data from a number of investigations 
by using the EQI to compare catalytic 
converter performance on engines tested 
with No. 2 diesel fuel. The results are 
shown in table 3. The percent of base- 
line columns in the table are determined 
by dividing the EQI for the exhaust con- 
trol by the EQI for the bare engine and 
multiplying by the percent of baseline 
for the bare engine. This amounts to 
defining the performance of the untreated 
indirect-injection engine as a unit of 
EQI. Catalytic converters increased the 
EQI in some cases by more than a factor 
of 2. The table shows the benefits are 
derived when converters are used with 
low-sulfur fuel and water scrubbers. 

Hunter (27) conducted tests to deter- 
mine the effect that a monolithic oxida- 
tive catalytic converter had on emissions 
from a Caterpillar 3208 diesel engine 
using No. 2 fuel. Test results from four 
steady-state engine modes, showed that 
large increases in the amounts of DPM and 
sulfates and reduction of the soluble 
organic fraction (SOF) occurs when con- 
verters are used. In the mode exhibit- 
ing the most extreme case, S0 4 emission 
increased from a fraction of gram per 
kilowatt hour to more than 2.5 g/kW'h as 
the exhaust passed through the catalyst. 
Similar results were obtained for the 
other three modes. 



TABLE 3. - Effect of catalytic converters on EQI 



Exhaust treatment 


DI engine 


IDI engine 




EQI 


Pet of baseline 


EQI 


Pet of baseline 




224 
314 
314 

102 

102 

103 

103 

74 

74 


113 
158 
158 

51 

51 

52 

52 

37 

37 


199 
484 
292 

197 
84 

197 
84 

133 

55 


100 




243 
147 


Monolithic converter plus 


99 


Pellet converter plus 

Monolithic converter plus 

water scrubber 1 

Pellet converter plus 


42 
99 
42 


Monolithic converter plus 
water scrubber and low- 


67 


Pellet converter plus 
water scrubber and low- 


28 



DI Direct-injection. 
'For coal operations, 
exhaust. 



IDI Indirect-injection. 

a water scrubber is required to cool the 



An explanation offered for the increase 
in DPM is that it is caused by the de- 
hydrogenation of the organic compounds 
present in the exhaust (27). This reac- 
tion results in the formation of solid 
carbon and low hydrogen-to-carbon ratio 
hydrocarbons. The fact that the S0F was 
decreased in all test modes is consistent 
with this explanation. 

A similar catalyst was tested (28) on a 
single-cylinder diesel engine operated 
under different conditions and a 70-pct 
reduction of both DPM and SOF was ob- 
tained when catalytic temperatures ex- 
ceeded 250° C. For polyaromatic HC and 
other high-molecular-weight compounds in 
the SOF, a 70-pct reduction was achieved 
at temperatures above 170° C. This re- 
sult was attributed to the high-molec- 
ular-weight compounds 
carbon particulate 
brought into direct 
catalyst surface. 

The effect of monolithic and pelletized 
catalytic converters on mutagen levels 
in a salt mine was assessed (29), and a 
fivefold increase in mutagen level was 
observed when the monolithic converter 
was used. This finding is similar to 



adsorbed onto the 

and thereby being 

contact with the 



laboratory data reported by Hunter (27). 
In Hunter's study the Ames bioassay 
showed that mutagenicity per gram of sol- 
uble organic material increased when the 
catalyst was used, but was partially off- 
set by a reduction in the mass of SOF 
emitted. 

The pelletized catalytic converter re- 
sulted in a thirtyfold increase in muta- 
gen levels over the untreated engine 
despite a substantial decrease in poly- 
nuclear aromatic HC. This decrease in 
polynuclear aromatic HC accompanied by an 
increase in mutagenic activity results 
from nitration of the polynuclear aro- 
matic HC, which are trapped and later 
released by the pelletized converter. 
Evidence suggests that very strong muta- 
gens such as the dinitropyrenes are 
formed (30-31 ). Even though there is no 
direct relationship between Ames activity 
and adverse health effects it has been 
recommended (32) that the Ames test and 
other in vitro tests be used to screen 
engineering alternatives and that the 
information obtained be combined with 
data from animal and epidemiological 
studies to aid in the decision making 
process. 



10 



CONCLUSIONS AND RECOMMENDATIONS 



1. Catalytic converters are effective 
in reducing CO, HC, and odors when the 
exhaust temperature remains above 250° C. 
Converter temperature is dependent upon 
engine duty cycle, and engines operating 
under moderate to heavy loads generally 
have high enough temperatures to allow 
efficient converter operation. 

2. Catalytic converters slightly in- 
crease N0 X emissions. 

3. Sulfate emissions are increased by 
the use of catalytic converters, but this 
increase can be offset by using fuel con- 
taining 0.1- pet sulfur or less. If low- 
sulfur fuels are not used, the increase 
in sulfate and N0 2 emissions can offset 
any advantages of the catalytic converter 
as measured by the EQI. 

4. Mutagenic activity of the SOF is 
increased when catalytic converters are 
used. 



Based upon criteria recommended by 
a joint Canadian-United States research 
panel (18) , catalytic converters should 
have very limited use in underground 
mines. Converters can reduce CO, HC, and 
odor emissions, but these reductions 
are frequently offset by increased lev- 
els of the more toxic pollutants, N0 2 
and sulfates, thus causing an increase 
in the EQI. In addition, studies have 
shown that catalytic converters produce 
soluble organic compounds with high muta- 
genic activity. Although mutagenic ac- 
tivity is not directly linked to adverse 
health effects, these assays have been 
recommended for screening engineering 
alternatives and mine operators should be 
aware of the results. Vehicles equipped 
with converters should operate under 
moderate- to heavy-load conditions and 
use fuel with a sulfur content less than 
0.1 pet. 



REFERENCES 



1. Daniel, J. H. , Jr. Diesels in Un- 
derground Mining: A Review and an Evalu- 
ation of an Air Quality Monitoring Meth- 
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2. Ogden, S. 0. Economics, Safety and 
Operating Advantages of Diesels in Under- 
ground Coal Mines. Min. Cong. J. , v. 64, 
No. 9, 1978, pp. 237-242. 

3. Richards, W. M. Switch to Cata- 
lytic Exhaust Purifiers Cuts Maintenance 
Costs at Copper Mine. Eng. Min. J. , v. 
176, No. 10, 1975, pp. 102-103. 

4. Partridge, P. A., F. J. Shala, 
N. P. Cernansky, and I. H. Suffet. Char- 
acterization and Analysis of Diesel Ex- 
haust Odor. Environ. Sci. Technol. , v. 
21, No. 4, 1987, pp. 403-408. 

5. Dainty, E. D. , A. Lawson, and J. P. 
Mogan. Synopsis of Contract Findings: 
The Ventilation Implications of the Re- 
duction of Diesel Emissions Toxicity by 
Water - in Oil Fuel Emulsif ication. CAN- 
MET, Energy, Mines and Resour. , Ontario, 



Canada, Report MRP/MRL 80-15(TR), Feb. 

1980, 32 pp. 

6. Johnson, J. H. , E. 0. Reinbold, 
and D. H. Carlson. The Engineering Con- 
trol of Diesel Pollutants in Underground 
Mining. SAE Tech. Pap. Series 810684, 

1981, 46 pp. 

7. Engelhard Corporation. Control 
of Diesel Exhaust Emissions in Under- 
ground Mines. Ongoing BuMines contract 
H0199029; for inf., contact E. D. Thim- 
ons, TP0, Dust Control and Ventilation 
Div. , BuMines, Pittsburgh, PA. 

8. Eccleston, B. H. , D. E. Seizinger, 
and J. M. Clingenpeel. Diesel Exhaust 
Emissions from Engines for Use in Under- 
ground Mines. Bartlesville Energy Tech- 
nology Center, Bartlesville, OK, DOE/ 
BETC/RI-80/6, Apr. 1981, 42 pp. 

9. Acres, J. K. Platinum Catalyst 
for Diesel Engine Exhaust Purification. 
Platinum Met. Rev., v. 14, No. 3, 1970, 
pp. 78-85. 



11 



10. Sercombe, E. J. Exhaust Purifiers 
for Compression Ignition Engines. Plati- 
num Met. Rev., v. 19-20, No. 1, 1975, 
pp. 2-11. 

11. Bykowski, B. B. Preliminary In- 
vestigation of Light-Duty Diesel Cata- 
lysts. Emission Control Technology Divi- 
sion, Ann Arbor, MI, EPA-460/3-80-002, 

1980, 45 pp. 

12. Fleming, R. D. , and T. R. French. 
Durability of Advanced Emission Controls 
for Heavy Duty Diesel and Gasoline Fueled 
Engines. Bartlesville, OK, EPA-460/3-73- 
010, 1973, 120 pp. 

13. Marshall, W. F., D. E. Seizinger, 
and R. W. Freedman. Effects of Catalytic 
Reactors on Diesel Exhaust Composition. 
BuMines TPR 105, 1978, 9 pp. 

14. Marshall, W. F. Emission Control 
for Diesels Operated Underground: Cata- 
lytic Converters. Bartlesville Energy 
Res. Centr. , Bartlesville, OK, BERC/RI- 
75/8, 1979, 10 pp. 

15. Lilly, L. C. R. (ed.). Part 2 - 
Engine Design Practice, Section 10 - Fuel 
Injection Systems in Diesel Engine Refer- 
ence Book. Butterworth, 1984, pp. 10-1 
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16. Institute of Machinery and Insti- 
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gewerkschaf tskasses. Verminderung des 
Gehaltes and schadlichen Bestandteilen in 
den Abgasen von Diselmotoren bei methan- 
haltiger Ansaugluft (Reduction in the 
Content of Noxious Constituents in the 
Exhausts of Diesel Engines with Methane- 
Containing Intake Air). Final Report, 

1981, 52 pp.; available for consultation 
at the Twin Cities Res. Cent. , Minne- 
apolis, MN. 

17. Mogan, J. P., and E. D. Dainty. 
Emission Control Performance of Diesel 
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Vol. 36, 1986, pp. 135-142. 

18. Schnakenberg, G. H. , Jr., J. P. 
Mogan, and E. W. Mitchell. Diesel Emis- 
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19. Ian W. French and Associates, Ltd. 
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tions of Exposure of Underground Mine 
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Ottawa, Canada, Apr. 20, 1984, 607 pp. 

20. American Conference of Governmen- 
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OH). TLV's-Threshold Limit Values for 
Chemical Substances in the Work Envi- 
ronment Adopted by ACGIH With Intended 
Changes for 1986-87. 1986, 111 pp. 

21. Schnakenberg, G. H. , Jr. Current 
State-of-the-Art of Diesel Emission Con- 
trol - An Overview. Ann. ACGIH, v. 4, 

1986, pp. 233-243. 

22. Watts, W. F., Jr. Industrial Hy- 
giene Issues Arising From the Use of 
Diesel Equipment in Underground Mines. 
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April 21, 1987, and Denver, CO, April 23, 

1987, comp. by Staff, BuMines. BuMines 
IC 9141, 1987, pp. 4-8. 

23. Daniel, J. H. , Jr. Carbon Diox- 
ide and an Index of Diesel Pollutants. 
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Proceedings: Bureau of Mines Technol- 
ogy Transfer Seminar, Louisville, KY, 
April 21, 1987, and Denver, CO, April 23, 
1987, comp. by Staff, BuMines. BuMines 
IC 9141, 1987, pp. 52-57. 

24. Mogan, J. P. , and E. D. Dainty. 
Development of the AQI/EQI Concept — A 
Ventilation Performance Standard for Die- 
selized Underground Mines. Ann. ACGIH, 
v. 14, 1987, pp. 245-247. 

25. Rehnberg, 0. Effects of Diesel 
Exhaust Catalytic Converters for Under- 
ground Use, Soc. Min. Eng. AIME, Trans., 
v. 1, 1981, pp. 1990-1994. 

26. Mogan, J. P. , and E. D. Dainty. 
Assessment of Diesel Exhaust Treatment 
Options by a New Diesel Ventilation Cri- 
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12 



27. Hunter, G. , J. 
bier, S. Bagley, D. Leddy 
J. Johnson. The Effect 
Catalyst on the Physical 
Biological Character of 
late Emissions. SAE Tec 
810263, 1981, 32 pp. 

28. Andrews, G. E. , 
Ejiofor, and S. W. Pang, 
late SOF Emissions Redu 
Exhaust Catalyst. SAE Te 
870251, 1987, pp. 103-112 

29. Mogan, J. P., E. 
Westaway, and A. J. Hort 
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Spec. vol. 36, 1986, pp. 



Scholl, F. Hib- 
, D. Abata, and 
of an Oxidation 
, Chemical, and 
Diesel Particu- 
h. Pap. Series 

I. E. Iheozor- 

Diesel Particu- 

ction Using an 

ch. Pap. Series 

• 

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ized Mines. CIM 
188-197. 



30. Mogan, 
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Friend or Foe 
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Vergeer, and 
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and Carcinoge 
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? CIM Spec. vol. 36, 1986, 

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13 



APPENDIX. —ABBREVIATIONS AND 

This listing does not include unit of 
measure abbreviations, which are listed 
after the table of contents, or abbrevi- 
ations that are used and identified in 
the tables. 

ACGIH - American Conference of Govern- 
mental Industrial Hygienists. 

AQI - Air quality index. 

DPM - Diesel particulate matter. 

EQI - Emissions quality index. 

LHD - Load-haul-dump. 

RCD - Respirable combustible dust. 

SOF - Soluble organic fraction. 

TLV - Threshold limit value. 



SYMBOLS USED IN THIS REPORT 

CO - Carbon monoxide. 
C0 2 - Carbon dioxide. 
HC - Hydrocarbon. 
H 2 S0 4 - Sulfuric acid. 
NO - Nitric oxide. 
N0 X - Oxides of nitrogen. 
N0 2 - Nitrogen dioxide. 



S0 X - Oxides of sulfur. 



50 2 - Sulfur dioxide. 

503 - Sulfur trioxide. 

50 4 - Sulfate. 



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